It is known that it is advantageous to connect an agricultural machine, especially a mower, to the front of a movable vehicle, such as a tractor. This allows any cut agricultural products, such as fodder, to pass between the wheels of the tractor, and also permits another machine to be connected to the rear of the tractor in a conventional fashion, with the result, that the tractor's mowing capacity is increased, time is saved, and its fuel consumption is reduced.
However certain regulations must be observed when connecting a machine to the front of a tractor. In fact, certain traffic legislation stipulates a maximum distance between the driver's place on the tractor, and the forward extremity of a machine connected to the front of a tractor. The object of this measure is to ensure good visibility when driving, particularly at road junctions.
Furthermore, when an agricultural machine is connected to the front of a tractor, it is advantageous for the machine to be located as close to the front wheels of the tractor as possible. The shorter the distance between the machine and the front wheels of the tractor, the easier it is for the machine to follow any unevennesses of the terrain.
The problem of causing a machine connected to the front of a tractor to follow the terrain is solved effectively by the use of a linking system of pivotable parallelogram means connected between the machine and attachment hooks or the like of the tractor.
A linking system of this type incorporating pivotable parallelogram means, whose bars are connected to a machine by means of cylindrical articulating devices and the pivotable bolts of which are horizontal, and extend at right angles to the direction of advance of the tractor, has a number of disadvantages.
In fact, the bars of the parallelograms extending towards the front and downwardly, as seen in the direction of advance of the machine, are connected to the machine at their lower ends, while their upper ends are connected to the attachment hooks or the like of the tractor. This method of connection increases the distance between the machine connection side of the tractor, and the forward part of the machine. Moreover, since the bars of the parallelograms are articulated or pivoted on cylindrical shafts, the machine connected to these bars is restrained to move only in a vertical plane within the movement restraints of the pivotable parallelogram mechanism.
As a result, in the event one end of the machine strikes an obstacle, while the machine is in its operative position, the entire machine will be lifted, maintaining its attitude within the constraints of the pivotable parallelogram mechanism, when passing over the obstacle. Thus, in the case of a mower connected to the front of a tractor, the grass or the fodder will not be cut as closely over the entire width of the machine. Whenever the machine passes over an obstacle, a swath of grass will remain, extending over the entire width of the machine, thus constituting a certain loss of the expected harvest, quite apart from the additional disadvantage of hindering fresh growth of the crop.
Furthermore, when the machine is lifted, it generally moves forwardly along an arc of a circle. But, when the machine encounters an obstacle, it should be lifted and move forwardly, even though the obstacle impedes this desired forward movement.
Finally, the aforedescribed connecting device has the drawback of stressing the cylindrical articulating means of the bars of the parallelograms to a considerable extent. These stresses occur principally when a change in the direction of motion is made, with the machine connected in its operable position to the tractor, which in turn, makes it necessary to use relatively large articulating means, which increases the weight and cost of the machine.